Featured Database Articles

Oracle Technical Interview Questions Answered - Part1 - Page 2

Technical - Oracle

This is the part you have all been waiting on. Please if you
have just skipped to this section, go back to the personal section and read it.
There is much to be gained by the personal section and conveying to your
interviewer who you are and how you tick from day to day. Also, the answers I
am giving here are off the cuff and are not intended to be the definitive
answer to these questions. There are many aspects to these questions that just cannot
be answered here and honestly, you will not have time to explain any of these
questions fully in the interview process. It is up to you to make sure your
interviewer understands that you understand the question and have given enough
information that they know you understand the concept.

1.
Explain
the difference between a hot backup and a cold backup and the benefits associated
with each.

A hot backup is basically taking a backup of the database
while it is still up and running and it must be in archive log mode. A cold
backup is taking a backup of the database while it is shut down and does not
require being in archive log mode. The benefit of taking a hot backup is that
the database is still available for use while the backup is occurring and you
can recover the database to any point in time. The benefit of taking a cold
backup is that it is typically easier to administer the backup and recovery
process. In addition, since you are taking cold backups the database does not
require being in archive log mode and thus there will be a slight performance
gain as the database is not cutting archive logs to disk.

2.
You
have just had to restore from backup and do not have any control files. How
would you go about bringing up this database?

I would create a text based backup control file,
stipulating where on disk all the data files where and then issue the recover command
with the using backup control file clause.

3.
How do
you switch from an init.ora file to a spfile?

Issue the create spfile from pfile command.

4.
Explain
the difference between a data block, an extent and a segment.

A data block is the smallest unit of logical storage for a
database object. As objects grow they take chunks of additional storage that
are composed of contiguous data blocks. These groupings of contiguous data
blocks are called extents. All the extents that an object takes when grouped together
are considered the segment of the database object.

5.
Give
two examples of how you might determine the structure of the table DEPT.

Use the describe command or use the dbms_metadata.get_ddl
package.

6.
Where
would you look for errors from the database engine?

In the alert log.

7.
Compare
and contrast TRUNCATE and DELETE for a table.

Both the truncate and delete command have the desired
outcome of getting rid of all the rows in a table. The difference between the
two is that the truncate command is a DDL operation and just moves the high
water mark and produces a now rollback. The delete command, on the other hand,
is a DML operation, which will produce a rollback and thus take longer to
complete.

8.
Give
the reasoning behind using an index.

Faster access to data blocks in a table.

9.
Give
the two types of tables involved in producing a star schema and the type of
data they hold.

Fact tables and dimension tables. A fact table contains
measurements while dimension tables will contain data that will help describe
the fact tables.

10.
. What
type of index should you use on a fact table?

A Bitmap index.

11.
Give
two examples of referential integrity constraints.

A primary key and a foreign key.

12.
A table
is classified as a parent table and you want to drop and re-create it. How
would you do this without affecting the children tables?

Disable the foreign key constraint to the parent, drop the
table, re-create the table, enable the foreign key constraint.

13.
Explain
the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits
and disadvantages to each.

ARCHIVELOG mode is a mode that you can put the database in
for creating a backup of all transactions that have occurred in the database so
that you can recover to any point in time. NOARCHIVELOG mode is basically the
absence of ARCHIVELOG mode and has the disadvantage of not being able to
recover to any point in time. NOARCHIVELOG mode does have the advantage of not
having to write transactions to an archive log and thus increases the performance
of the database slightly.

14.
What
command would you use to create a backup control file?

Alter database backup control file to trace.

15.
Give
the stages of instance startup to a usable state where normal users may access
it.

STARTUP NOMOUNT - Instance startup

STARTUP MOUNT - The database is mounted

STARTUP OPEN - The database is opened

16.
What
column differentiates the V$ views to the GV$ views and how?

The INST_ID column which indicates the instance in a RAC
environment the information came from.

17.
How
would you go about generating an EXPLAIN plan?

Create a plan table with utlxplan.sql.

Use the explain plan set statement_id = 'tst1' into plan_table
for a SQL statement

Look at the explain plan with utlxplp.sql or utlxpls.sql

18.
How
would you go about increasing the buffer cache hit ratio?

Use the buffer cache advisory over a given workload and
then query the v$db_cache_advice table. If a change was necessary then I would
use the alter system set db_cache_size command.

19.
Explain
an ORA-01555

You get this error when you get a snapshot too old within
rollback. It can usually be solved by increasing the undo retention or
increasing the size of rollbacks. You should also look at the logic involved in
the application getting the error message.

20.
Explain
the difference between $ORACLE_HOME and $ORACLE_BASE.

ORACLE_BASE is the root directory for oracle. ORACLE_HOME
located beneath ORACLE_BASE is where the oracle products reside.

Well, we
have gone through the first 25 questions as I would answer them during an
interview. Please feel free to add your personal experiences to the answers as
it will always improve the process and add your particular touch. As always remember
these are "core" DBA questions and not necessarily related to the
Oracle options that you may encounter in some interviews. Take a close look at
the requirements for any job and try to come up with questions that the
interviewer may ask. Next time we will tackle the rest of the questions. Until
then, good luck with the process.